In the mission Drive-Thru, when the second cutscene begins after the quartet arrives at the drive-thru, Ryder, Sweet, and Big Smoke's models can be seen stacked on top of one another in a T pose. The characters spawn there as part of their role in the cutscene, but were placed away from the Greenwood for an unknown reason. When the camera cuts to CJ pulling up to the drive-thru, the other gang members teleport into the Greenwood and play their animation like usual.
The Scarecrow probably only exists in the game because of a developer oversight. The original versions of GTA San Andreas were designed for use on 4:3 monitors and television screens, where that part of the screen would be covered up by black bars or not visible at all. Expanding the visible area causes the characters to appear, and the developers did not bother to fix the issue. Because of this, the glitch can only be seen in later ports of the game that include a widescreen mode, including the Xbox 360 and PC versions.